Ambrosia artemisiifolia in the Czech Republic: history of invasion,current distribution and prediction of future spread

Ambrosia artemisiifolia v České republice – historie invaze, současné rozšíření a predikce dalšího šíření

Hana S k á l o v á1, Wen-Yong G u o1, Jan W i l d1,2 & Petr P y š e k1,3

1Institute of Botany, The Czech Academy of Sciences, Zámek 1, CZ-252 43 Průhonice,

Czech Republic, e-mail: hana.skalova@ibot.cas.cz, guowyhgy@gmail.com, jan.wild@

ibot.cas.cz, pysek@ibot.cas.cz; 2 Faculty of Environmental Sciences, Czech University of

Life Sciences Prague, Kamýcká 129, Praha 6 – Suchdol, CZ-165 21, Czech Republic;3Department of Ecology, Faculty of Science, Charles University, Viničná 7, CZ-128 44

Prague, Czech Republic

Skálová H., Guo W.-Y., Wild J. & Pyšek P. (2017): Ambrosia artemisiifolia in the Czech Repub-lic: history of invasion, current distribution and prediction of future spread. – Preslia 89: 1–16.

We analyse the dynamics of invasion of Ambrosia artemisiifolia (common ragweed), one of themost noxious invasive species in Europe with a great impact on human health. We investigate thehabitats and factors that shape its current distribution and specify areas in the Czech Republicendangered by the further spread of this species. The analysis is based on a total of 281 records in164 grid cells, recorded up to 2016, of which 37 harbour naturalized populations and 127 casualpopulations. The majority of records (49%) was from railway corridors, followed by human set-tlements (11%), and there was a recent increase in records from roadsides. A conditional infer-ence tree revealed factors shaping the species distribution with the effect of the proportional areaof industrial, commercial and transport units as the most important, highly significant variable,further fine-tuned by factors related to human-related dispersal and climate, such as densityof railway network and temperature, respectively. The prediction model indicated that manysuitable grid cells are unoccupied. Many of these grid cells are in the proximity of currently occu-pied ones but there are also some cells rather far from current populations. Further spread ofA. artemisiifolia in the Czech Republic is thus highly probable.

K e y w o r d s: common ragweed, Czech Republic, environmental factors, plant invasion, pre-dicted spread, species distribution modelling (SDM)

Introduction

Predicting the future distribution of alien plants and the role that specific pathways anddrivers are likely to play in this process in the context of the ongoing global climatechange are among the highest priorities of invasion biologists and managers (e.g. Thuilleret al. 2005, Gallien et al. 2010, Essl et al. 2015a, Uden et al. 2015). Understanding thedrivers that influence the spatiotemporal patterns in plant invasions is a crucial step inlimiting their spread and minimizing their negative impact (Ewel et al. 1999, Sakai et al.2001, Pyšek & Hulme 2005). This is especially true for rapidly spreading species thathave a great impact on native biodiversity and human health (Pyšek & Richardson 2010,Essl et al. 2015b, Pergl et al. 2016). However, the relative influence of individual drivers,such as human-mediated disturbance and changing climate, is unknown for most invasive

Preslia 89: 1–16, 2017 1

doi: 10.23855/preslia.2017.001

plants and hence limits the effectiveness of risk assessments and adaptive management(Uden et al. 2015).

Ambrosia artemisiifolia L. (common ragweed) is an annual herbaceous plant thatoriginates from North America and is one of the most noxious invasive species in Europe(Lambdon et al. 2008, DAISIE 2009) mainly because it produces large quantities of aller-genic pollen (Kazinczi et al. 2008) and causes up to 80% loss in the yield of certain crops(Essl et al. 2015b). It is strongly self-incompatible with high outcrossing rates (see Essl etal. 2015b and the references herein). The species only reproduces by seed, with an aver-age of 1213 seeds per plant reported for the Czech Republic (Moravcová et al. 2010), andbetween 18,000 and 48,000 (with an extreme value of 94,900) for Hungary (Essl et al.2015b). Most seed falls within 1 m of the mother plant (Essl et al. 2015b). Seed dispersalby mammals and birds is reported in its native range (Rosas et al. 2008), but there is littleevidence of seed dispersal by animals in Europe (Bullock et al. 2012). Dispersal of seedsby water is uncommon (Fumanal et al. 2007). The long-distance seed dispersal is primar-ily through human activities; either directly by the transport of contaminated litter or soil,or indirectly as a contaminant of agricultural products (e.g. crops and bird feed) or agri-cultural and construction machinery that is then inadvertently distributed along transportcorridors (see Bullock et al. 2012 and the references herein). Ambrosia artemisiifolia

forms a persistent seed bank in soil and is able to germinate after 40 years (Darlington1922). Seed dormancy is broken by low (winter) temperatures under wet conditions(Willemsen 1975, Baskin & Baskin 1987, Fumanal et al. 2006).

Ambrosia artemisiifolia was originally introduced into Europe in the 18th centurythrough botanical gardens (DAISIE 2009, Bullock et al. 2012), and then repeatedly asa contaminant of agricultural products from North America (Brandes & Nitzsche 2006,Chauvel et al. 2006). The species began to spread and naturalize within Europe from the1930s, these processes accelerated from the 1960s and since the 1990s there has beena rapid spread and increase in abundance of local invasive populations (Essl et al. 2015b).The largest, recently-recorded European populations are on the Pannonian Plains of Hun-gary and in Croatia, Serbia and Ukraine (Essl et al. 2015b). In Russia, naturalized popula-tions are recorded in 10 regions in the GloNAF global database of naturalized alien floras(van Kleunen et al. 2015), ranging from the western part of the country eastwards toKhabarovsk. A considerable increase in abundance is also recorded in southern and cen-tral France, in particular along the Rhône valley and on the plains of northern Italy(Chauvel et al. 2006, Essl et al. 2015b). It is predicted that it will spread further in Europe,favoured by ongoing global warming; the species is assumed to benefit from warmersummers and absence of late autumn frosts (Cunze et al. 2013, Richter et al. 2013a, Chap-man et al. 2014, Storkey et al. 2014, Leiblein-Wild et al. 2016). In contrast, some regions,especially in the south, are predicted to become unsuitable due to the increase in theincidence of summer droughts and temperature (Jacob et al. 2013).

As local scale variation in soil characteristics and anthropogenic factors are thought tointeract with the effect of climate change on the distributions of plant species(Stratonovitch et al. 2012, Guo et al. 2013), not only climate needs to be taken into accountwhen predicting the future spread of A. artemisiifolia. However, factors other than climateare investigated only occasionally and over a limited area in analyses of A. artemisiifolia

distribution. Besides climatic factors, landscape variables explain the current distribution

2 Preslia 89: 1–16, 2017

of A. artemisiifolia in Austria (Essl et al. 2009) and soil characteristics, position withina field and crop type and cover in arable fields in Hungary (Pinke et al. 2011, 2013).

To extend the knowledge about the occurrence and distribution of A. artemisiifolia inEurope, and demonstrate that such information can be used to predict future trends, weanalyse records from the Czech Republic. In this country the species was first reported in1883 (see Pyšek et al. 2012a, b), with early records originating from agricultural fields inthe southern and western part of the country where it was probably introduced with con-taminated seeds. The first record from Moravia, the eastern part of the country, wasreported in 1948. The species was sometimes cultivated in botanical gardens (Jehlík1998). The number of records (see Pyšek et al. 2012a for a detailed account of the situa-tion in the Czech Republic) has been rapidly increasing since the second half of the 20thcentury (Williamson et al. 2005). However, the factors that have facilitated its invasion inthe Czech Republic are unknown and need to be understood if future risks are to be iden-tified and effective management strategies developed to reduce the spread and impact ofthis species.

In this paper we address the following questions: (i) What were the pathways of inva-sion by A. artemisiifolia in the Czech Republic and do the invasion dynamics of thisspecies differ in different habitats? (ii) What is the proportion of sites with casual versusnaturalized populations, and under what conditions are the former likely to progress intothe latter? (iii) Which climatic and landscape factors shape the current distributionof this species? (iv) Which parts of the Czech Republic are likely to be colonized byA. artemisiifolia in the future?

Materials and methods

Study area

The Czech Republic, a central-European country with an area of 78,864 km2 and popula-tion of 10.6 million, is prone to invasions by plants due to its position on the crossroads ofmany natural and human-created migration routes, which provide dispersal opportunitiesand pathways. In addition, a heterogeneous landscape and long history of human influ-ence provides a variety of disturbed sites that are suitable for establishment of alien plants(see Pyšek et al. 2012a for details). These features, together with a strong botanical tradi-tion, make the country a suitable model for studying and predicting regional patterns inplant invasions (Pyšek et al. 2002, 2012a, b, Chytrý et al. 2005, 2009).

Data collection

Botanical records of A. artemisiifolia in the Czech Republic up to July 2016 were col-lected from various sources: Czech National Phytosociological Database (Chytrý &Rafajová 2003); Species Occurrence Database held by the Nature Conservation Agencyof the Czech Republic (http://www.ochranaprirody.cz); a database of the distribution ofvascular plants in the Czech Republic (FLDOK, Štepánek unpubl.); public and privateherbaria; other literature sources and unpublished records (e.g. Williamson et al. 2005).The records (281 in total) were, based on their location, assigned to nine types of habitat:arable fields; countryside (unmanaged sites in open landscape where the species occurs,

Skálová et al.: Ambrosia artemisiifolia in the Czech Republic 3

such as ponds and river banks, pedestrian paths, seminatural grasslands); industrial areas;other agricultural areas; railways; river harbours; roads; settlements; and others) and to 5'× 3' grid cells (longitude × latitude, ~32 km2 at 50° northern latitude) of KFME(Kartierung der Flora Mitteleuropas of 2551 cells for the Czech Republic; Schönfelder1999). Cells were further categorized according to the stage in the invasion process thatbest represented the A. artemisiifolia record(s) (Richardson et al. 2000, Blackburn et al.2011): (i) naturalized, for grid cells with a population of more than 50 individuals orrecords for at least 5 years or at least 5 sites, or records for 3–4 years and 3–4 sites, (ii)casual, for grid cells that did not meet the above criteria, or the population size and otherdetails are unknown, (iii) absence. Each cell was characterized by climatic data andanthropogenic variables such as density of transport corridors and land use (ElectronicAppendix 1).

Data analysis

Analysis of covariance (ANCOVA) was used to test the difference in the cumulativenumber of A. artemisiifolia records for particular habitats, with year as a covariate. Thedata was log-transformed to meet the assumptions of the analysis and the models werefurther checked and confirmed by diagnostic plots.

Decision tree models, which are also known as classification and regression trees(Breiman et al. 1984, De’ath & Fabricius 2000), were used to identify the most importantpredictors for the presence of A. artemisiifolia in individual 5' × 3' grid cells within theCzech Republic. As a non-parametric statistical method, decision tree models can handledata with a non-normal distribution, mixed types of data and non-linear relationships, andthe results from the models are easy to interpret (Breiman et al. 1984, De’ath & Fabricius2000, Pinke et al. 2011). To compensate for the overfitting of traditional decision treemodels, the conditional inference tree implements a permutation test at each split to sta-tistically determine when the model should stop (Hothorn et al. 2006, Strobl et al. 2009).The conditional inference tree was constructed with the ctree function in the party pack-age (Strobl et al. 2009) in R (version 3. 2. 5, R Core Team 2016).

Species distribution modelling (SDM) was used to assess the likelihood of A. artemisii-

folia occurring in the Czech Republic under current conditions. SDMs develop statisticalconnections between known presence of the species and environmental variables, andthey can then map the connections to geographical space (Elith & Leathwick 2009).SDMs are frequently used in predicting hotspots of rare and endangered species and thepotential spread of invasive species (Thuiller et al. 2005). Grid cells harbouring popula-tions classified as casual and/or naturalized were counted as presence. We used pseudo-absence data randomly selected from all absence grid cells. Two pseudo-absence datasetswith 200 absences for each dataset were generated. We used an ensemble method to over-come the variability in SDM models and maximize the usefulness of the multiple models(Araújo & New 2007). Seven modelling algorithms were used in the ensemble proce-dure: artificial neutral network (ANN), classification tree analysis (CTA), generalizedboosting model (GBM), generalized linear model (GLM), maximum entropy (Maxent),multiple adaptive regression splines (MARS) and random forest (RF). All models werecalibrated via 10-fold cross-validation by randomly splitting the data into two subsets:training data (70%) and test data (30%). The default settings of each model were used.

4 Preslia 89: 1–16, 2017

Two evaluate measures, TSS (Allouche et al. 2006) and AUC (Fielding & Bell 1997,Phillips & Dudík 2008), were calculated. Models with TSS greater than 0.5 and ROClarger than 0.8 were included in the ensemble models (Allouche et al. 2006, Phillips &Dudík 2008, Thuiller et al. 2009). All SDMs and ensemble models were constructedusing the BIOMOD2 package (Thuiller et al. 2009, 2012) in R (R Core Team 2016). Thesuitable habitat maps were presented in ArcGIS 10.3 (Environmental Systems ResearchInstitute, Redlands, CA).

Results

Total number of records and frequency in different habitats

The first two records of A. artemisiifolia in the Czech Republic (both in 1883) were fol-lowed by a lag phase. It was not until the 1950s that a rather sharp increase in the numberof records and occupied grid cells occurred (Fig. 1). The first grid cell with a naturalizedpopulation was recorded in 1962, and the number of such grids increased dramaticallyafter 2005. Up to 2016 there were a total of 281 records in 164 grid cells. Of these gridcells, 37 harboured naturalized populations and 127 harboured casual populations.

Despite the first records coming from arable fields, the number of records in this typeof habitat increased rather slowly (Fig. 2). About half of the records are from railway cor-ridors, both historically and currently (49% of all records). Human settlements are thesecond most frequently colonized habitat (11% of all records). Another trend is the veryrecent increase in the cumulative number of records from roadsides (Fig. 2). However,the regression slopes of the cumulative records by year for railway corridors, settlementsand roadsides do not differ significantly (Electronic Appendix 2), indicating that the rateof spread of A. artemisiifolia over time in these habitats was similar.

Skálová et al.: Ambrosia artemisiifolia in the Czech Republic 5

0

50

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1875 1900 1925 1950 1975 2000 2025

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Fig. 1. – Cumulative number of � records, �� occupied grid cells and � grid cells with naturalized populations(i.e. with populations of more than 50 individuals or records for 5 or more years; or records from 5 sites or morewithin the cell; or records from 3–4 years and from 3–4 sites within a cell) of Ambrosia artemisiifolia in theCzech Republic since the first record up to 2016.

Factors shaping the distribution of Ambrosia artemisiifolia

A conditional inference tree identified the proportion of industrial, commercial and trans-port areas within cells as the strongest predictor of A. artemisiifolia presence (Fig. 3,Electronic Appendix 3). Ambrosia artemisiifolia is highly likely to be present in gridcells with more than 3.1% of their area covered by this type of habitat. The pattern is fine-tuned by the relative influence of other covariates; regardless of the proportion of indus-trial, commercial and transport areas, grid cells with a high density of railway network aremore likely to harbour A. artemisiifolia populations than those with fewer railways.Another important influence on whether populations remain as casual or become natural-ized is the annual temperature. Populations in grid cells with a mean annual temperatureabove 9.4 °C and dense railway networks, or mean temperatures above 9.1 °C and moder-ately dense rail networks in areas with less than 30% of agricultural landscapes, are likelyto become naturalized. Populations in grid cells below these thresholds are likely to becasual occurrence(s) (Fig. 3).

Within grid cells where the proportional area of industrial, commercial and transportunits are below 3.1% and the railway network is sparse, there is an extremely low proba-bility of the occurrence of Ambrosia if the total length of water streams and January

6 Preslia 89: 1–16, 2017

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Fig. 2. – Cumulative number of records of Ambrosia artemisiifolia from particular habitats in the CzechRepublic up to 2016.

Skálová et al.: Ambrosia artemisiifolia in the Czech Republic 7

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temperature are low (Fig. 3). Moreover, the proportion of industrial, commercial andtransport area below 10.2%, in combination with low density of railways, results in zeroprobability of harbouring naturalized populations (Electronic Appendix 3). As a result,most A. artemisiifolia populations, especially naturalized ones, are recorded along theLabe river (eastern, northern and central Bohemia), south-east of Brno (southern Moravia)and close to the town of Ostrava (north-eastern Moravia and Silesia) (Fig. 4).

Potential distribution of Ambrosia artemisiifolia in the Czech Republic

The prediction model (Fig. 5) revealed more than half of the country (56% of grid cells;Table 1) is of very low suitability for A. artemisiifolia. However, the model also indicatesthat many grid cells with suitable conditions are currently unoccupied; more than half ofthose with the most suitable conditions are not colonized, and only about one quarter ofthese cells host naturalized populations. Many unoccupied grid cells in close proximity tooccupied cells were assessed as having a high suitability (Fig. 5). This suitability is espe-cially true for cells in northern, central and eastern Bohemia along the Labe river, in east-ern Moravia along Morava and Odra rivers, in northern and central Bohemia in the sur-roundings of big cities such as Ústí nad Labem and Prague, respectively, and in north-eastern and southern Moravia in the surroundings of Ostrava and Brno. However, somehighly suitable cells are rather far from currently occurring populations, especially thosein western Bohemia along the Ohře river and west of the city of Plzeň, and also in south-ern Bohemia close to České Budějovice. In contrast, suitable cells that are far from cur-rently occurring populations are rather rare in Moravia.

Table 1. – Percentage of grid cells in the Czech Republic within individual probability categories as revealed bythe prediction model, percentage of cells within the categories that are occupied by Ambrosia artemisiifolia

and percentage of cells with naturalized populations.

Occurrenceprobability category

% total cells % occupied % with a naturalizedpopulation

0.04–0.2 56.3 0.3 0.10.2–0.4 17.1 3.9 0.00.4–0.6 14.1 8.1 0.60.6–0.8 5.0 24.6 6.40.8–0.94 7.5 43.5 15.7

Discussion

Total number of records and frequency in particular habitats

Ambrosia artemisiifolia was first recorded in the territory of the present-day CzechRepublic in the same year as it was in the territory of the present-day Austria (Essl et al.2009). However, the rate of spread in the Czech Republic was considerably slower than inAustria. Despite the countries being of comparable size, the current number of recordsand occupied grid cells in the Czech Republic is only about 40% of those recordedin Austria up to 2009 (Essl et al. 2009). Although it is not possible to make a detailed

8 Preslia 89: 1–16, 2017

Skálová et al.: Ambrosia artemisiifolia in the Czech Republic 9

Fig. 4. – Map showing the distribution of Ambrosia artemisiifolia in the Czech Republic displayed togetherwith (A) distribution of mean annual temperature in 5' × 3' grid cells and river networks, and (B) distribution ofproportional area of industrial, commercial and transport units in 5' × 3' grid cells and railway networks.

comparison with other countries due to the absence of detailed data, it is clear that theextent of the area colonized in the Czech Republic is considerably less than in Hungary,Croatia and Serbia (Kazinczi et al. 2008).

The high number of records associated with transport corridors, railways and roads, istypical of the occurrence of A. artemisiifolia in the Czech Republic, Slovakia and Austria.The Czech Republic has more records from railway corridors and there was about a 10-year delay in the start of the rapid spread along roads. These routes seem to have becomethe main transport pathway of A. artemisiifolia in the Czech Republic just as in other cen-tral-European countries (Vitalos & Karrer 2009, Jolly et al. 2011, Medvecká et al. 2012,Milakovic et al. 2014, Essl et al. 2015b, Hrabovský et al. 2016, Milakovic & Karrer2016). The situation may be similar to Slovakia where the number of ragweed recordsstarted to increase markedly around 2010, namely along highways and main roads(Hrabovský et al. 2016). The spatiotemporal pattern in the Czech Republic also supportsthe view of reported long-distance dispersal as a contaminant of crops or bird feed, directtransport of contaminated litter or soil or attached to construction- or agricultural machin-ery (Bullock et al. 2012). Populations in arable fields are now rather scarce. This could bea result of rather low propagule pressure due to the existence of a limited number of reallyextensive populations in the Czech Republic, lower seed production compared to othercountries (Moravcová et al. 2010, Essl et al. 2015b) and still low abundance along roadsthat may serve as a stepping stone for the invasion of fields. However, the situation maysoon change due to the ongoing spread of A. artemisiifolia along roads that are managed

10 Preslia 89: 1–16, 2017

Fig. 5. – Potential distribution of Ambrosia artemisiifolia in grid cells (5'× 3') in the Czech Republic based onfactors revealed by the conditional interference tree as shaping the species distribution with up to now recordedoccurrences represented by dots.

using agricultural machinery for cutting the roadsides and cleaning ditches. If popula-tions become established on arable land, further spread by agricultural machinery seemsinevitable, and may follow the trend reported from Hungary where A. artemisiifolia

became the most abundant weed in less than 50 years and is now present in all grid cells(Pinke et al. 2011). The large-scale establishment of A. artemisiifolia in this habitat posesa major threat due to the increase in propagule pressure, which consequently is likely toaccelerate the invasion in climatically suitable areas at the regional scale. Another possi-ble stepping stone in this invasion could be forest nurseries where plants were recentlyrecorded (J. Doležal, personal observation). Ambrosia artemisiifolia seed and seedlingscan be easily distributed with young trees.

Factors shaping the distribution of Ambrosia artemisiifolia

Predominance of records from sites with frequent, mainly anthropogenic disturbancereflects the poor competitive ability of A. artemisiifolia (Leskovšek et al. 2012). The poorresistance of the species to spontaneous succession (Gentili et al. 2015) and populationdecline at disturbance-free sites indicates the crucial role of disturbance in maintainingthe populations. In our analysis, the role of disturbance manifests itself through the asso-ciation with particular types of habitats, with the proportion of area that is industrial,commercial and related to transport being the most important variable shaping the currentdistribution of A. artemisiifolia in the Czech Republic. Its effect is further fine-tuned byfactors related to human-related dispersal and climate, such as density of the railway net-work and temperature, respectively. This fact should be taken in account when construct-ing models of its future distribution. Surprisingly, the anthropogenic factors are rarelyincluded in models of A. artemisiifolia distribution (but see Richter et al. 2013a, b),despite their importance demonstrated in previous studies of common ragweed (Essl etal. 2009) and other species (Stratonovitch et al. 2012, Guo et al. 2013). Anthropogenicfactors may explain the differences in distribution predicted by our models and those ofother authors who identified the western part of the Czech Republic as the most suitablearea (Cunze et al. 2013, Storkey et al. 2014), or did not predict the occurrence of the spe-cies in northern Moravia (Leiblein-Wild et al. 2016).

Although temperature is not the most important factor influencing the distribution ofA. artemisiifolia, it played a key role in the past in determining the invasion pathways andthe likelihood of naturalization once sites are colonized. This factor was identified as themain splitter between the two stages of the invasion process (following the terminologyof Richardson et al. 2000, Blackburn et al. 2011). This is in accordance with experimen-tally demonstrated effect of low temperature in slowing down the rate of seed germina-tion (Leiblein-Wild et al. 2014) and development of seedlings (Skálová et al. 2015) andleaves (Deen et al. 1998). The negative effect of low temperature may be partly compen-sated by an increased nutrient availability (Skálová et al. 2015), which may explain theoccurrence at disturbed sites (where nutrient availability is usually high) and facilitatefurther spread into arable fields.

Potential distribution of Ambrosia artemisiifolia in the Czech Republic

Our models indicate that not all sites suitable for A. artemisiifolia are already invaded.Further spread within the Czech Republic is thus probable. At the local scale it is likely that

Skálová et al.: Ambrosia artemisiifolia in the Czech Republic 11

populations will colonize suitable areas in the proximity of sites of current occurrence,but there is also a great potential for long-distance spread to remote areas. In some areasthe spread might be limited by low precipitation as this was revealed as a limiting factorin previous studies (Pinke et al. 2011, Jacob et al. 2013). The occurrence of a single plantdoes not necessarily result in the establishment of a population due to pollen limitationand strong self-incompatibility (Essl et al. 2015b). However, the presence of additionalindividuals may result in stable populations and the formation of a viable, long-lived seedbank (Darlington 1922). This provides an opportunity for populations to survive overtime (Gioria et al. 2012, Gioria & Pyšek 2016). At such sites the vegetation cover shouldnot be destroyed as more disturbed, open habitats allow ragweed populations to recover(H. Skálová & L. Moravcová, personal observation). The spread may be slowed down bythe eradication of newly emerging individuals or populations. At infested sites distur-bance should be avoided and sowing of seed mixtures composed of competitively strongspecies is recommended (Gentili et al. 2015). Populations at permanently disturbed sitessuch as roadsides should be managed by precisely timed cutting, which is reported toreduce seed production (Milakovic et al. 2014).

See www.preslia.cz for Electronic Appendices 1–3

Acknowledgments

Our thanks are due to people who provided field records, mainly Jan Doležal, Karel Fajmon, Jan W. Jongepier,Zdeňka Lososová, Radomír Němec, Antonín Reiter, Kateřina Šumberová and Anna Volejníková, to ZuzanaSixtová for technical assistance, Jasmin Packer and Tony Dixon for language revision and Milan Chytrý andthree anonymous reviewers for valuable comments on the text. This study was supported by project LD15157from Ministry of Education, Youth and Sports of the Czech Republic, long-term research development projectRVO 67985939 (The Czech Academy of Sciences), and project no. 14-36079G, Centre of ExcellencePLADIAS (Czech Science Foundation). We also acknowledge support from EU COST Action FA1203 ‘Sus-tainable management of Ambrosia artemisiifolia in Europe (SMARTER)’.

Souhrn

Analyzovali jsme dynamiku šíření jednoho z nejnebezpečnějších invazních druhů, Ambrosia artemisiifolia,který je znám svým dopadem na lidské zdraví. Studovali jsme ji s ohledem na biotopy a faktory, které určujíjeho současné rozšíření, a vytipovali jsme oblasti, které jsou ohroženy jeho dalším šířením. Analýza vychází z dosa-vadních 281 záznamů výskytu získaných do roku 2016, situovaných ve 164 mapovacích polích, z nichž 37 hostínaturalizované populace a 127 populace přechodně zavlečené. Nejvíce záznamů pochází z blízkosti železnič-ních koridorů (49 %), za nimiž následují lidská sídla (11 %). Zaznamenali jsme nárůst výskytu druhu podél sil-nic během posledních let. Analýza pomocí dedukčního regresního stromu ukázala, že rozšíření druhu je nejví-ce ovlivněno procentním zastoupením průmyslových, komerčních a transportních ploch v mapovacím poli.Vliv mají také faktory související s transportem diaspor zprostředkovaným lidskou činností, jako je hustota že-lezniční sítě, a z klimatických faktorů průměrná teplota v mapovacím poli. Predikční model ukázal, že zdalekane všechna vyhovující pole jsou již obsazena. Značná část těchto polí se nachází v těsné blízkosti těch již obsa-zených, ale identifikovali jsme i pole, která splňují stejná kritéria jako ta již obsazená a přitom se od nich nachá-zejí ve značné vzdálenosti. V České republice lze proto předpokládat další šíření ambrózie peřenolisté.

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Received 15 November 2016Revision received 7 December 2016

Accepted 20 December 2016

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